1. Field of the Invention
The present invention relates to a data communication device that carries out serial communication in order to control a motor, which is connected via an inverter to a DC link part connected to an alternating-current power source via a converter, by carrying out switching of a switching element included in either the converter or the inverter for each fixed switching period, from the time when the preparation of driving the motor is completed to the time when the motor is stopped.
2. Description of Related Art
A data communication device, which functions a master device or a slave device that carries out serial communication in order to control a motor in a system, which includes motors to drive a feed axis and a main axis of a machine tool, an industrial robot arm, etc., is proposed.
In such a system which includes the motors, the master device is implemented by a converter control device configured to control a converter in order to convert alternating-current power supplied from an alternating-current power source into direct-current power, an upper control device such as a CNC (computer numerical control), etc., and the slave device is implemented by an inverter control device configured to control an inverter in order to convert the direct-current power which is converted by a converter into alternating-current power, etc. For example, in the case where the master device is the converter control device and the slave device is the inverter control device, data such as status information, alarm information, etc., is shared between the converter control device and the inverter control device by carrying out data transmission and reception via a serial communication bus. In the case where the master device is the upper control device and the slave device is the inverter control device, data such as motor position or speed command data of, etc., is transmitted from the upper control device to the inverter control device via the serial communication bus and data such as current value data, motor position or speed data, etc., is transmitted from the inverter control device to the upper control device via the serial communication bus, thereby the data is shared between the converter control device and the inverter control device.
A serial communication among a plurality of devices can transmit and receive an amount of data larger than the amount of data that can be transmitted and received by parallel communication with electric lines in a number smaller than the number of electric lines used for the parallel communication (for example, two electric lines are used in the case of I2C communication).
When controlling a motor, there is a possibility that an anomaly may occur in data transmitted or received by the master device or the slave device due to switching noise caused by switching of a switching element, which is included in an equipment (for example, inverter) controlled by at least one of a master device and a slave device, for each fixed switching period, from the time when the preparation of driving the motor is completed to the time when the motor is stopped.
A data communication device, which avoids the influence of the switching noise by detecting the switching of a switching element and displacing the timing to transfer data from an encoder from the time of switching of the switching element in order to avoid the influence of the switching noise on the data transmitted or received by the master device or the slave device, is proposed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2006-20374 (JP2006-20374A), and a data communication device, which avoids the influence of the switching noise by detecting the switching of the switching element and temporarily suspending the system clock at the time of switching of the switching element in order not to transmit or receive data, is proposed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2010-88186 (JP2010-88186A).
However, in the conventional data communication device, it is necessary to use a dedicated switching detection circuit in order to detect the switching of the switching element, and therefore the cost of the data communication device increases.